The present invention pertains to the field of powered roller screeds used to screed cementitious material.
Concrete structures are formed by pouring a cementitious material, such as cement and aggregate (comprising concrete slurry) into a form, or other container, and permitting the material to cure under proper conditions. In the case of a. concrete pad, such as a floor, foundation, or roadway, concrete is poured onto a ground, or support, surface and contained by forms connected to, and rising above, the ground surface. The forms are longitudinal members arranged along a border of a desired location for the concrete pad to contain the viscous concrete and provide a guide for the concrete""s thickness and to level the top surface of the concrete.
After concrete is poured between forms, it is spread evenly between the forms. A screed is then used to remove excess concrete and level the top surface of the concrete so it is even with the forms. Often, several passes of a screed over the concrete is necessary to achieve the desired surface. Precision is required to conform to building codes and to perform quality work.
A very primitive screed, which is still useful on small jobs, is a simple straight edge such as a straight board. The board, chosen long enough to span the forms, is laid on top of each form and thereafter worked side-to-side and pulled down the length of the forms by workers at each end of the board. This process pushes forward excess concrete: excess concrete is concrete that is higher than the top surface of the forms. While quite suitable for small jobs, such a screed is impractical on large jobs because of the work required to move the excess concrete.
A more practical screed for larger jobs is disclosed in Mitchell, U.S. Pat. No. 4,142,816. Mitchell discloses a powered screed having a hydraulic motor to spin a tubular member while the screed is pulled along the forms by two workers, one each located on either side of the forms. As with most rotary screeds, the tubular member spins in a direction opposite a direction of travel of the screed. By spinning the tube, this screed provides a good surface to the concrete. However, substantial work is required to pull the screed along the forms. The hydraulic motor, spinning the tube, does not assist to propel the screed forward and the heavy concrete that builds up in front of the screed requires a large amount of force to move. In addition, workers located at each end of the Mitchell screed must keep the screed tube substantially perpendicular to the formsxe2x80x94frequently this is a difficult task because of uneven amounts of concrete from side-to-side and unequal strengths of the workers.
Larger, powered screeds are suitable for large, high-volume jobs. U.S. Pat. No. 5,456,549 discloses a powered rotary screed having a modular frame that spans across concrete-retaining forms to support a strike tube and drive tubes. The frame provides rigidity and support so that the screed can span large distances between forms. The strike tube rotates opposite the direction of screed travel to screed the concrete and the drive tubes provide motive force to propel the screed.. While very useful for large jobs, and jobs that are not constrained by space limitations, these larger screeds are difficult to use in close quarters and are more difficult to transport.
Accordingly, there is a need in the industry to provide a powered screed that can be easily controlled during use, and conveniently transported and set up for use.
The present invention provides a frameless roller screed having two tubes: a strike tube and a drive tube. The strike tube is located at a leading edge of the screed and is made to rotate so as to oppose the direction of motion of the screed. The strike tube contacts rough laid concrete to level the concrete to the height of the forms and finish the surface of the concrete. The rotational motion of the. screed tube provides a better quality finish to the concrete surface than can be achieved with a non-rotating strike tube or a strike tube that rotates in the direction of travel.
In preferred embodiments, the drive tube of the present invention is a split drive tube having independently controlled portions that provide superior control of the screed during operation. The drive tube is split into first and second drive tube portions that are separately controlled by the operator so that left and right ends of the screed may be independently driven to adjust for misalignment that may occur as the screed moves along the forms. Oftentimes, uneven concrete will present uneven resistance to the screed and impede the forward progress of the screed on one side, thereby misaligning the screed on the forms. The split drive tube of the present invention permits the operator to adjust the motive power at one end of the screed relative to the other end so as to compensate for such misalignment.
In preferred embodiments, the first and second drive tube portions are cylindrical and the two portions are axially aligned and coupled. The drive tube portions are coupled so as rotate independently of each other and each portion is separately driven to permit separate control of the respective portions.
Preferably, hydraulic motors drive the strike tube and the drive tube. The strike tube is powered by a single motor for control of the rotational speed and direction of rotation of the strike tube.
The drive tube is powered by two motors. One motor controls each one of the respective two drive portions, thus allowing separate control of the first and second drive portions as to rotational speed and direction of rotation.
In addition, the screed includes handles located on opposite ends of the screed that are arranged as levers to assist with control of the screed. The handles are coupled to the screed such that an operator can push a distal end of the handle downward, or raise the distal end upward, to lever the drive tube about the strike tube. Pushing down on the handle tends to lift the drive tube off of the forms so that forward motion of the screed may be easily, and quickly, halted. Alternatively, lifting the handles places more of the screed""s weight on the drive tube and increases the drive tube""s pressure on the forms so that the drive tube can provide more motive force without slipping.
Using the handles as the primary means to control the screed during operation requires trained operators at each end of the screed. However, by providing the drive tube as a split drive tube, as disclosed in the present invention, allows one person control and operation of the screed.
The roller tubes of the present invention are coupled together by plates located on distal ends of the screed. The screed has no frame that extends substantially over the concrete, or spans the forms.
Accordingly, the present invention provides a frameless, powered rotary screed having a split drive tube with separately controllable ends that permit the screed operator to control the screed""s motive force at, each end separately to adjust for uneven concrete and prevent skewing of the screed on the forms.